The present invention relates to a thermocompressing bonding method for electrically and mechanically connecting electronic components such as printed circuit boards and the like using a thermosetting type anisotropic conductive adhesive film.
In recent years, when two printed circuit boards having conductor patterns are to be connected to each other, thermocompressing bonding for connecting them using an anisotropic conductive adhesive film is used. More specifically, according to thermocompressing bonding, when a circuit board having a plurality of parallel conductor patterns and another circuit board having a plurality of parallel conductor patterns at the same pitch as that of the former circuit board are to be electrically and mechanically connected to each other, these circuit boards are arranged so that the conductor patterns face to each other, and a thermosetting anisotropic conductive adhesive film is interposed between these two conductor patterns. In this state, a thermocompressing head applies heat and pressure to the circuit boards and adhesive film from the side above one circuit board. Thus, the anisotropic conductive adhesive film establishes conductivity in its thickness direction, so that the circuit boards are mechanically and electrically connected to each other.
A thermosetting type anisotropic conductive adhesive film is prepared by dispersing metal fine particles (Ni, carbon) in a thermosetting resin film. The thermosetting type anisotropic conductive adhesive film hardens after the resin softens by heating/compressing, thereby mechanically connecting the circuit boards to each other, and the metal fine particles dispersed in the resin form conductive structures, thereby electrically connecting the conductor patterns to each other.
As typical methods of applying heat and pressure in thermocompression bonding, a constant heat method, and pulse heat method are known.
According to the constant heat method, the temperature of the thermocompressing head is maintained constant during the thermocompression bonding process, and a compression force is applied to the circuit boards for a predetermined period of time, thereby changing the temperature of the anisotropic conductive adhesive film.
According to the pulse heat method, a thermocompressing head nearly concurrently applies heat (at a predetermined temperature) and a compression force to the circuit boards for a predetermined period of time, thereby changing the temperature of the anisotropic conductive adhesive film by means of Joule heat produced at that time.
With the constant heat method, thermocompression bonding can be realized by a relatively inexpensive apparatus. However, the freedom of temperature control is low, so that it is difficult to obtain suitable temperature waveforms with respect to a various types of objects.
With the pulse heat method, since the freedom of temperature control is high, a suitable temperature waveform can be easily selected.
However, in the pulse heat method, since the temperature of the thermocompressing head rises quickly, the anisotropic conductive adhesive film abruptly melts and spreads. Thus, the compression force applied to the circuit boards and adhesive film lowers abruptly, so that it is difficult to suppress the thermal expansion of the circuit boards, thereby causing positional shifts of the circuit boards. Further, positional shifts of the circuit boards are also caused by the lowering of the compression force applied to the circuit boards.
Such positional shift of the circuit boards results in electrical connection errors between the conductor patterns, thus considerably impairing the reliability of electrical connections.
The present invention has been made in consideration of the above situation, and has as its object to provide a thermocompression bonding method and apparatus, which can assure stable electrical and mechanical connections between electronic components without causing any positional shift.
In order to achieve the above object, according to the present invention, in a thermocompression bonding method a thermosetting type anisotropic conductive adhesive is interposed between first and second conductors and the first and second conductors are electrically and mechanically connected to each other by applying heat and pressure from the side above the first and second conductors; thermocompression bonding is attained by slowly raising the temperature of the anisotropic conductive adhesive up to its thermosetting end temperature.
In this case, the compression force to be applied to the anisotropic conductive adhesive is raised abruptly, and the temperature of the anisotropic conductive adhesive is slowly increased up to the thermosetting end temperature.
According to the present invention, in a thermocompression bonding method in which a thermosetting type anisotropic conductive adhesive is interposed between first and second conductors and the first and second conductors are electrically and mechanically connected to each other by applying heat and pressure from the side above the first and second conductors; the anisotropic conductive adhesive is instantaneously heated to the softening start temperature, and thereafter, is slowly heated up to the hardening end temperature.
As described above, with the thermocompression bonding method according to the present invention, since the heating temperature of the anisotropic conductive adhesive is slowly increased to the hardening end temperature, the anisotropic conductive adhesive can be prevented from abruptly melting and receding. As a consequence, the compression force applied to the first and second conductors can be prevented from lowering abruptly, and hence, positional shifts between the first and second conductors can be prevented.
Furthermore, a thermocompression bonding method according to the present invention comprises the steps of: stacking conductors of first and second electronic components with interposing a thermosetting type anisotropic conductive adhesive therebetween; applying a pressure to the anisotropic conductive adhesive via one of the first and second electronic components by using a thermocompression bonding head, which produces Joule heat in accordance with a current applied thereto; and supplying a current, which is based on a setting voltage waveform including a first level region, a second level region higher than the first level, and an inclined region between the first and second level regions, to the thermocompression bonding head while applying the pressure, to slowly heat the anisotropic conductive adhesive to a thermosetting end temperature thereof so as to harden the anisotropic conductive adhesive after it softens, thereby thermocompression bonding the conductors of the first and second electronic components by the anisotropic conductive adhesive.
A thermocompression bonding apparatus according to the present invention comprises: a thermocompression bonding head for producing Joule heat in accordance with a current supplied thereto; pressing means for pressing the thermocompression bonding head against one of first and second electronic components which are stacked to sandwich a thermosetting type anisotropic conductive adhesive between conductors thereof, and applying a predetermined pressure to the anisotropic conductive adhesive via one of the first and second electronic components; and current supply means for supplying, to the thermocompression bonding head, a current which is based on a setting voltage waveform including a first level region, a second level region higher than the first level, and an inclined region between the first and second level regions.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.